Use current event set rather than current pending change when deciding whether to...

Use current event set rather than current pending change when deciding whether to no-op a del

This alters event_changelist_del to quash deletion of events that
didn't exist in the first place.

As far as I can see, the add,delete, dispatch case described in the
original comment will never happen.  The recorded change is a single
operation, not a queue.  This seems to leave actions to delete
events that never existed as the real targets for no-oping